The Cell Theory

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THE CELL THEORY

A. All living organisms are made up of one or more cells

B. The cell is the basic unit of life

C. All cells come from the division of pre-existing cells

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HEAD LICE

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HANDS AND CLAWS OF A HOUSEFLY

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MARINE POLYCHAETE WORM, NEREIS

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Wasp

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Pollen

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TRYPANOSOME

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BORRELIA BURGDORFERI (CAUSES LYME DISEASE)

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White Blood Cell

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Head of the malaria vector mosquito Anopheles gambiae

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Eyelashes

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Salmonella

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Salmonella

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Velcro

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EUKARYOTIC CELLS: THE ANIMAL CELL

EUKARYOTIC CELLS: THE PLANT CELL

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THE FLUID MOSAIC MODEL Cells are surrounded by a thin membrane of lipid

and protein, about 100 angstroms (100 x 10-10 m) thick.

The cell membrane is a remarkable structure that has properties of a solid and a liquid.

It forms a "fluid sea" in which proteins and other molecules like other lipids or carbohydrates are suspended (like icebergs) or anchored at various points on its surface.

the “sea” or “fluid” part is composed of side by side phospholipids arranged in a bilayer (called a lipid bilayer).

The solid part (the “mosaic”) is the variety of proteins etc. embedded in the bilayer.

Selectively permeable (will let some substance in but not other the same size)

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EACH PHOSPHOLIPID HAS A HYDROPHOBIC TAIL AND A HYDROPHILIC HEAD

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PLANT CELLS Plant Cells also have a Cell Wall

surrounding their cell membrane. the cell wall is made up of a large

number of cellulose fibers cemented together (like the cellulose fibers in paper). Small molecules have little difficulty penetrating the cell wall, while larger molecules may not be able to pass through. (the cell wall is said to be semi-permeable)

Cell Wall

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THE NUCLEUS the nucleus is a large, centrally located

organelle surrounded by nuclear envelope. The nuclear envelope is a double membrane (2 phospholipid bilayers thick) that has pores in it for molecules to enter and exit).

The envelope is very porous and is a continuation of the membranes of the endoplasmic reticulum.

The pores, called nuclear pores, allow selected molecules into and out of the nucleus.

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NUCLEUS

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FUNCTION OF THE NUCLEUS Control center or "brain" of cell. Contains the

DNA and is site of manufacture of RNA. The DNA is contained by a number of chromosomes, which consist of long strands of DNA tightly wound into coils with proteins called histones. The combination of DNA and histone proteins is known as CHROMATIN. Chromosomes function in packaging of DNA during nuclear division and control of gene expression

The nucleus, therefore, determines the metabolism, growth, differentiation, structure, and reproduction of cell.

The nucleus contains one or more DARK-STAINING discrete structures, known as NUCLEOLI, which are sites of RIBOSOMAL RIBONUCLEIC ACID (rRNA) SYNTHESIS.

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ENDOPLASMIC RETICULUM (ER) the ER is a system of MEMBRANOUS TUBULAR

CANALS that begins just outside the nucleus and branches throughout the cytoplasm.

if ribosomes are attached to the ER, it is called ROUGH Endoplasmic Reticulum. The function of rough ER is protein synthesis.

if no ribosomes are attached to the ER, it is called SMOOTH Endoplasmic Reticulum. The function of smooth ER is synthesis of lipids

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ENDOPLASMIC RETICULUM

RoughE.R.

Smooth E.R.

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ER FUNCTION The endoplasmic reticulum membranes

provide an increase in surface area where chemical reactions can occur.

The channels of the reticulum provide both storage space for products synthesized by the cell and transportation routes through which material can travel through other parts of the cell. The endoplasmic reticulum is also the cell's membrane factory. Phospholipids and cholesterol, the main components of membranes throughout the cell, are synthesized in the smooth ER.

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GOLGI BODIES Most of the proteins leaving the

endoplasmic reticulum are still not mature. They must undergo further processing in another organelle, the Golgi apparatus, before they are ready to perform their functions within or outside the cell.

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The Golgi Apparatus, named after an Italian anatomist of the nineteenth century, are stacks of flattened, hollow cavities enclosed by membranes, which are often continuous with the membranes of the endoplasmic reticulum.

located near to the nucleus and ER. The stack is made of a half-dozen or

more saccuoles. Looks like a flattened stack of hollow tubes. Each sac in the organelle contains enzymes that modify proteins as they pass through.

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Thus, the Golgi apparatus functions in modification, assembly, packaging, storage and secretion of substances.

it receives newly manufactured protein (from the ER) on it's inner surface. Within the Golgi apparatus, the proteins are sorted out, labeled, and packaged into vesicles that "pinch off" the outer surface of the saccuoles. These vesicles can then be transported to where they are needed within the cell, or can move to the cell membrane for export to the outside of the cell by exocytosis.

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RIBOSOMES consist of rRNA and proteins each ribosome is made of 2 non-

identical subunits rRNA is produced in the nucleolus and

joined with proteins -- then migrate through the nuclear pore to the cytoplasm for final assembly

ribosomes attach themselves to the endoplasmic reticulum

function is site for PROTEIN SYNTHESIS

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POLYSOMES free-floating

structures within the cytoplasm

generally produce proteins that will be used inside the cell

consist of clusters of ribosomes bunched together, each of which is transcribing the same type of protein

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VACUOLES AND VESICLES: STORAGE DEPOTS A VESICLE is a small vacuole vacuoles and vesicles are formed by: 1) pinching off from the Golgi apparatus 2) endocytosis of the cell membrane 3) extension of the ER membrane (for

example, the large central vacuole of a plant cell).

are used for transport and storage of materials

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PLANT CELLS USUALLY HAVE ONE LARGE CENTRAL VACUOLE

The plant cell’s central vacuole functions in:

1) water storage 2) food storage 3) waste storage 4) cell support

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LYSOSOMES: CELLULAR “STOMACHS” Special vesicles which are formed by

the Golgi apparatus. Contain powerful hydrolytic enzymes Functions in:

Cellular digestion Autodigestion or disposal of damaged cell

components like mitochondria Breakdown of a whole cell (by releasing

their contents into the cell cytoplasm). For this reason, they are sometimes called “suicide sacs.”

Destroying invading bacteria Lysosomes are known to contain over 40

different enzymes that can digest almost anything in the cell, including proteins, RNA, DNA, and carbohydrates.

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MITOCHONDRION

a.________________

b.________________

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MITOCHONDRIA: THE CELL’S POWERHOUSE

Mitochondria are the largest organelles in an animal cell, after the nucleus.

Are sausage-shaped or filamentous structures surrounded by a double-layered membrane

The mitochondrion has two membranes: an outer and an inner. The inner is convoluted into shelf-like folds called cristae. The enzymes responsible for cellular respiration are arranged, in assembly-line fashion, on the cristae. This is where energy is produced.

A cross-section of a mitochondrion.

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function is AEROBIC ENERGY METABOLISM (also called CELLULAR RESPIRATION). Converts glucose and fatty acids to ATP, the cell's primary energy molecule, as well as lesser amounts of other energy rich molecules. The overall formula for cellular respiration is:

C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY (i.e. 38 molecules of ATP)

a.________________

b.________________

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MORE FUNCTIONS Besides supplying energy, mitochondria

also help control the concentration of water, calcium, and other charged particles (ions) in the cytoplasm.

Mitochondria have some of their own DNA molecules and ribosomes that resemble those of prokaryotic cells.

Human mitochondrial DNA is a closed, circular molecule 16,569 nucleotide pairs long.

Mitochondria are also self-replicating. They "reproduce" by splitting in half (“binary fission”)

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mitochondria may have evolved from bacteria that once developed a close relationship with primitive eukaryotic cells, and then lost the capacity to live outside the cell.

Another interesting characteristic of human mitochondria is fact that all of a person's mitochondria are descendants of those of his or her mother.

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CHLOROPLAST Double-membrane bound organelles in

which PHOTOSYNTHESIS (the conversion of light energy to carbohydrates) occurs.

inside the chloroplast are membranous stacks of grana (look like pancakes!) where the chlorophyll is located. Each pancake is call a thylakoid.

Chlorophyll is the chemical that absorbs the energy of the sun to provide the energy required for reducing CO2 to Glucose.

Process is basically the opposite of cellular respiration:

CO2 + H2O + ENERGY (i.e. ATP) Carbohydrate + O2

A chloroplast

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THE CYTOSKELETON The network of

filamentous proteins structures within the cell that help it maintain shape, anchor organelles, or help the organelles move as necessary.

The primary constituents of the cytoskeleton are microtubules and microfilaments.

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MICROTUBULES & MICROFILAMENTS Microtubules are hollow, cylindrical

aggregates of tubelike structure that help give the cell shape and form; they are also involved in other cell processes.

made up of 13 rows of globular proteins arranged to form a hollow tube serve in moving materials within the cell, cell movement, cytoskeleton structure.

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MICROFILAMENTS Microfilaments are long, thin, contractile

rods that appear to be responsible for the movement of cells (both external and internal movement).

made up of double filaments arranged in a helical pattern, with each filament consisting of numerous globular proteins joined together.

serve in anchoring organelles and moving them within the cell, cell movement, cytoskeleton structure.

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EukaryoticStructure Prokaryotic Animal Plant

Cell Membrane YES YES YESCell Wall YES NO YESNucleus NO YES YESMitochondria NO YES YESChloroplasts NO NO YESER NO YES YESRibosomes YES, (small) YES, large YES, largeVacuoles NO YES, small YESLysosomes NO YES, usually NO, usuallyCytoskeleton NO YES YESCentrioles NO YES NO

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THE SURFACE AREA TO VOLUME RATIO & CELL SIZE

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Cells cannot get too large. When cells get too large, they must divide. One of the main reasons that cells do this is because of the way that a cell's volume changes with respect to its cell surface area.

S.A.=6 mm2S.A.=24 mm2

V = 1 mm3V = 8 mm3

SA:V = 6:1 SA:V = 3:1

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As the size of a cell increases, its surface to volume ratio decreases. This means that, as a cell gets larger, each cubic unit of cytoplasm is serviced by proportionally less cell membrane.

Cell Size

Surface area

Vol-ume

SA:V ratio

1 6 1 6:1

2 24 8 3:1

4 96 64 1.5:1

8 384 512 0.75:1

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SIGNIFICANCE Cells rely on diffusion for materials (such as

nutrients) to get into the cell. Diffusion is not a highly rapid or efficient means of distributing materials over long cellular distances. No portion of even the largest active cells is more than 1 mm from the cell membrane.

How do cells get around the limits of the surface to volume ratio?

1. Divide2. Slow down metabolism: e.g. unfertilized chicken

eggs3. Get long and thin rather than round and fat:

e.g. nerve cells4. Folds in the cell membrane: e.g. microvilli of

intestinal epithelial cells

THE CELL MEMBRANE

A closer look.

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The cell membrane is the gateway into the cell, and must allow needed things such as nutrients into the cell without letting them escape. In the same way, it must allow wastes to leave the cell. A wide variety of molecules and substances must pass through the cell membrane -- large, small, hydrophobic, hydrophilic. Molecules of the same size must sorted out, and the cell must also be able to get large amounts of molecules in and out when necessary. How can the cell membrane accomplish this?

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The answer lies in its structure. We already know about the FLUID MOSAIC MODEL of membrane structure. Why is it given that name?

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THE FLUID MOSAIC MODEL proteins wholly or partly embedded in

phospholipid bilayer forms mosaic pattern. carbohydrates strung together in chains are

attached to proteins ("glycoproteins") or lipids ("glycolipids") of membrane. Function as identification markers for cell recognition (helps immune system identify which cells belong to body and which are invaders).

is SELECTIVELY PERMEABLE: some molecules enter the cell, while other molecules (which can be the same size) are not allowed to enter. The cell membrane can discriminate between different molecules that are the same size!

all living cells, whether plant, animal, fungal, protozoan, or bacterial, are surrounded by cell membranes

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THERE ARE THREE GENERAL MEANS BY WHICH SUBSTANCE CAN ENTER AND EXIT CELLS:

Name Examples

1. DIFFUSION lipid-soluble molecules (e.g. alcohol, steroid hormones), water (via osmosis), gases (CO2, O2)

2. TRANSPORT BY CARRIERS (active and facilitated transport)

Sugars (e.g. glucose), amino acids, ions (e.g. Ca++, Na+, Cl-)

3. ENDOCYTOSIS AND EXOCYTOSIS (e.g. pinocytosis and phagocytosis)

macromolecules (e.g. proteins), cells or subcellular material

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DIFFUSION diffusion is a physical process that

can be observed with any type of particle. A UNIVERSAL PHENOMENON.

Law of Diffusion: particles MOVE FROM THE AREA OF GREATER CONCENTRATION TO THE AREA OF LESSER CONCENTRATION UNTIL EQUALLY DISTRIBUTED.

BEFORE AFTER

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movement by diffusion requires no energy to be added (although adding energy (i.e. heat) will speed it up).

diffusion is a slow process. The rate of diffusion is affected by the concentration gradient (the difference in concentration of the diffusing molecules between the two regions), the size & shape of the molecules, and the temperature. Diffusion in liquid is slower than in gas.

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Simple Diffusion

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THREE WAYS OF INCREASING THE RATE OF DIFFUSION:1. increase the temperature2. increase the concentration gradient3. decrease the size of the diffusing

molecules

water diffuses readily across membrane, through charged, protein-lined pores in the membrane (remember, water is not lipid-soluble) that will not allow anything else but water through. This is called OSMOSIS.

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SO WHAT GETS INTO CELLS BY DIFFUSION?

1. lipid-soluble molecules (e.g. alcohol, steroid hormones)

2. water (via osmosis)3. gases (CO2, O2)

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OSMOSIS the net movement of water molecules

from the area of greater concentration to the area of lesser concentration across a selectively-permeable membrane. x

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Explain what wouldhappen to the

concentrations ofwater, glucose, andcopper sulphate on

side A of thisexperiment.

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Osmosis – Water Moves from where it is more concentrated to where it is less concentrated

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Cells may be placed in solutions that contain the same number of solute molecules per volume as the cell (= isotonic solution), a greater number of solute molecules per volume (= hypertonic solution), or a lesser number of solute molecules per volume than the cell (= hypotonic solution).

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SUMMARY OF WHAT HAPPENS TO ANIMAL CELLS PLACED IN DIFFERENT TONICITIES OF SOLUTION:

Tonicity of Solution Cell is Put Into

Net Movement of Water

Effect on Cell

Isotonic

No net movement

Remains the same

Hypotonic

Cell gains water

H O2

Cell Swells & May Burst

“lysis”

Hypertonic

Cell loses water

H O2

Cell Shrinks

“crenation”

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TRANSPORT BY CARRIERS

FACILITATED TRANSPORT utilizes PROTEIN CARRIERS in cell

membrane to control passage of molecules in and out of cell.

are highly specific - each carrier passes only one type molecule

molecules only pass along concentration gradient.

REQUIRES NO ENERGY - is like diffusion in this sense

explains how lipid-insoluble molecules like GLUCOSE and AMINO ACIDS cross the cell membrane.

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FACILITATED TRANSPORTBEFORE FACILITATED TRANSPORT

OUTSIDE CELL INSIDE CELL OUTSIDE CELL INSIDE CELL

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ACTIVE TRANSPORT also performed by protein carriers REQUIRES ENERGY (ATP) moves molecules against the

concentration gradient (i.e. in the opposite direction of diffusion).

molecules move from area of lower concentration to area of higher concentration.

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BEFORE

OUTSIDE CELL INSIDE CELL

ACTIVE TRANSPORT

OUTSIDE CELL INSIDE CELL

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e.g. Iodine & Thyroid Gland. [I+] is low in blood, high in Thyroid Gland. Active Transport moves I+ from blood to thyroid.

e.g. Na+ actively transported out of urine by kidney tubule cells

e.g. sodium/potassium pump in nerve/muscle cells (see text). Moves Na+ from inside to outside of cell, and K+ from outside to inside.

e.g. Na+ Cl- and cystic fibrosis - a genetic disease, usually fatal, caused by blockage of Cl- transport.

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ENDOCYTOSIS AND EXOCYTOSIS another way to get molecules,

especially large particles, in and out of cell.

ENDOCYTOSIS: cell membrane forms a vesicle around the substance to be taken in.

Phagocytosis: what you call endocytosis if particles taken in really large (like other cells - e.g. human macrophages). Can be see with light microscope.

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Pinocytosis: (= cell drinking) - same idea as phagocytosis, except smaller particles taken in (requires electron microscope to see).

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ENDOCYTOSIS

Nu

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EXOCYTOSIS Reverse of endocytosis. Vacuole

within cell fuses with cell membrane and the vacuole contents are deposited on the outside. Important in secretion and excretion in cells.